1. Field of the Invention
The present invention relates to an optometric apparatus for a subjective examination of a visual function of an examinee's eye.
2. Description of Related Art
There is an optometric apparatus provided with a pair of right-and-left lens chamber units in each of which rotary disks are disposed, each disk mounting therein various types of optical elements (a spherical lens, a cylindrical lens, and an auxiliary lens such as a prism and a filter).
Each optical element provided in the conventional optometric apparatus of the above type is 20 mm in diameter (19 mm in effective diameter). However, when an examinee views an examination optotype through the optical element of such size, accommodation by a peeping effect (so-called mechanical myopia) may intervene, which causes an inaccurate examination result. After the examination using the above optometric apparatus, therefore, a trial frame examination using a trial lens of a relatively larger size is generally conducted. As a result, it would take much time to get through the examination.
The arrangement of the optical elements in each disk is, for example, as shown in FIG. 10. The structure in FIG. 10 includes two disks for the spherical lenses, two disks for the cylindrical lenses, and two disks for the auxiliary lenses. For instance, with regard to the spherical lens disks, two lenses one each of which is selected from eleven spherical lenses arranged in each disk can produce powers (diopters) of −19.00D to +16.75D in increments of 0.25D. A shielding plate (BL) to be used in an examination for one eye is arranged in the auxiliary lens disk which is the fifth disk far from the examinee's eye. However, this arrangement of the shielding plate would allow disturbance light to enter the inside of the lens chamber unit through a test window disposed on the examinee's eye side. Accordingly, movements of the optical elements (disks) disposed on the near side of the shielding plate to the examinee's eye and a superfluous internal structure could be seen by the examinee. Thus, the examinee might feel so uncomfortable as to have trouble in concentrating on the examination.